drm/i915/perf: pass stream to vfuncs when possible

We want to use some of the properties of the perf stream to program
the hardware in a later commit.

v2: Pass only perf stream as argument (Matthew)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181023100707.31738-4-lionel.g.landwerlin@intel.com